Oscillation generator for low frequencies



Patented Feb. 11, 1947 ZAEJNB eras OFFIC USCILLATION GENERA'IUR FUR LUV? FREQUENCIES Benjamin S. Vilkomerson, Qamden, N. 5., assignor to Radio Corporation of America, a corporation of Delaware Application February 19, 1944, Serial No. 523,064

oscillation generator which possesses suitable characteristics for generating a relatively undistorted sine wave having great frequency stability but comparatively low power. One of the difficulties encourtered in the past in designing a suitable circuit to meet the needs which my invention now supplies has been due to the fact that the resonant circuit of a push-pull generator was required to carry the direct current which is applied to the anodes of the discharge tube. Where such a resonant circuit included an iron core inductance, it was not possible to obtain the pure sine wave that was required, due to phase shift.

In carrying out my invention, the circuit com ponents are so arranged that no direct current ilows through the i on core inductance of the frequency determining element. Furthermore, the resonant circuit which I employ is so loosely coupled to the tube electrodes that the variations of anode current have negligible efiect in distorting he wave form of the oscillations generated.

My invention will now be described in further detail, reference being made to the accompanying drawing, the sole figure of which shows a circuit arrangement of a preferred embodiment.

Referring to the drawing I show an electron discharge tube which may, if desired, be a twin triode tube. One triode section comprises the cathode 2, the anode 3, and a control grid The other triode section comprises the cathode 2, the anode 5, and a control grid ii. Anode potential is supplied from any suitable source, indicated at +13, and this source of potential is connected to a movable tap on a potentiometer i which interconnects the two anodes 3 and 5.

The common cathode 2 is connected through a variable cathode resistor 8 to ground, the negative terminal of the direct current source being understood to be grounded.

Two feedback circuits are shown. One of these circuits is connected between the anode 3 and ground. It traverses a capacitor 9 and the series path of resistors it, it, and it. The junction between resistors ii and i2 is connected to the control grid 6. Another feedback circuit is con nected between the anode 5 and ground, this cir cuit including capacitor l3 and resistors I i, l5, and it. The junction between resistors i5 and IE5 is connected to control grid l.

The frequency determining circuit includes an 3 Claims. (Cl. 25036) adjustable capacitor ll which is parallel-connected to the primary winding it of an iron core transformer L9. This transformer has a secondary it which is preferably used in the output circuit. The terminals of the resonant circuit ll, 58 are connected respectively to each of the two feedback circuits at points where the resonant circuit will be effective in controlling the osci1-' lations generated, and also where tube electrode currents will be of negligible efiect upon the wave form of the oscillations. These connecting points are shown respectively as the junction between resistors it and it, also the junction between resistors it and 5.

The manner in which oscillations are generated will be well understood by those skilled in the art. It should be noted, however, that the inductance i8 carries no direct current. Further more, there is no need for an iron core choke to be interposed between the oscillation generator circuit and the direct current source. Therefore, no appreciable distortion results from current variations in the windings of the iron core transformer N.

In an embodiment of my invention which has been constructed and put to practical use, the potentiometer 1 had an overall resistance of 1 megohm, and the potentiometer tap was made adjustable in order to compensate for variations in the characteristics of the two triode sections. It will, of course, be understood that in place of the twin triode tube, two separate triode tubes might be used, in which case the variations might be greater, and hence would increase the need for a balancing adjustment on the potentiometer l in order to restore symmetry.

In the aforementioned actual embodiment of my invention, it might be well to state that other circuit parameters were selected as follows: the value of each of the resistors I and it was 59,000 ohms. Each of the resistors i! and I5 was rated at .5 megohm and the resistors l2 and it each had a value of 2 megohms. The cathode resistor 8 was variable between 0 and 50,000 ohms. The direct current source delivered volts. Capacitors 9 and 53 each had a value of .01 mid.

Of course, it is to be understood that the circuit constants can be varied within wide limits without departing from the spirit and. scope of the invention. Other modifications of my novel circuit arrangement may also suggest themselves to those skilled in the art.

I claim:

1. An oscillation generator comprising two discharge paths each extending from a cathode to an anode and each under control of a grid, means for supplying direct current potentials to the electrodes appropriate to each discharge path, said means including a direct current source and a potentiometer interconnecting the anodes and having a movable tap connected to the positive terminal of said source, the negative terminal of said source being connected to a cathode resistor having a grounded terminal and a terminal connected to both cathodes, impedance means for supplying feedback potentials from each anode of one path to the control grid of the other path, and thence to the cathode resistor terminal remote from the cathodes, each said impedance means including a blocking condenser and a voltage divider, and a parallel-resonant circuit connected across points of the two respective voltage dividers chosen for minimizing the distortion of the sine wave to be generated, said circuit being ofthe type having an iron core inductance, each grid being connected to its respective voltage divider at a point chosen for obtaining the optimum amplitude and phase of grid control potential.

2. A system for generating substantially undistorted sine waves, comprising two discharge devices each having a cathode, a control grid and an anode, means including a capacitor and a voltage divider for coupling the anode of each device to the grid of the other device respectively, each said voltage divider being extended from its grid connection to ground, a cathode resistor having a grounded terminal and a terminal connected to both cathodes, a direct current source having its negative terminal grounded and its positive terminal connected through a potentiometer to each of said anodes, said potentiometer being of the order of one megohm in value and forming an interconnection between the anodes and having its movable tap connected to said positive source terminal, an iron core transformer the primary winding of which is connected across symmetrically disposed points on said voltage dividers which are suitably chosen to provide satisfactory distribution of output power between that required for feedback and that required for the load, the secondary winding of said transformer being connected to said load, and a capacitor connected in parallel with the transformer primary and forming therewith a resonant circuit tuned to the frequency to be generated.

3. An oscillation generator comprising a pair of electron discharge devices each having an anode, a cathode and a grid, a circuit for subjecting said anodes to a positive voltage with respect to said cathodes, a condenser in series with a resistor connecting the anode of one system to the grid of the other, another condenser in series with another resistor connecting the anode of the other system with the grid of the one system, resistors connected between the grids and cathodes, a parallel tuned circuit consisting of an iron cored coil and a condenser in shunt therewith, and connections from terminals on said tuned circuit to the resistors connected between the anodes and grids of said electron discharge devices, said tuned circuit connections being arranged to prevent the flow of direct current through said iron cored coil.

BENJAMIN S. VILKOMERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,973,303 Appleton Sept. 11, 1934 2,079,134 Terman May 4, 1937 OTHER REFERENCES A Low Distortion Audio-Frequency Oscillator, by Herbert J. Reich, I. R. E., vol. 25, No. 11, November 1937, pp. 1387-1938. 250-36-7.1. 

